Our objective is to examine a new approach for the treatment of choroidal melanoma. The research is designed to determine the efficacy of using porphyrin photodynamic therapy to selectively destroy the choroidal blood vessels supplying choroidal melanomas. There is considerable evidence that photodynamic therapy (PDT) can effectively destroy blood vessels in both tumor tissue and normal tissue. It is therefore possible that the choroidal vascular bed supplying choroidal melanomas can be selectively destroyed by PDT using either trans-scleral light delivery (in treating peripheral tumors) or by trans-pupillary light delivery for photocoagulative PDT (in treating posterior tumors). Both light delivery procedures will be evaluated. The porphyrin to be used in all PDT studies is Photofrin II and red light (630 nm) generated by an argon pumped dye laser will be used for photochemical activation of Photofrin II. The pigmented rabbit and the amelanotic Greene's melanoma (transplanted to the choroid) will be our animal and tumor model. The specific aims of this research proposal are: 1) to determine the PDT treatment parameters required to produce localized and complete choroidal vessel destruction, and to document the type and extent of acute and chronic ocular toxicity (both in and out of the treatment field) induced by these treatments. Ophthalmoscopic observation, fundus photography, fluorescein angiograph and histopathological examinations will be performed; 2) to assess the ability of PDT (directed at the choroidal blood vessels) to successfully destroy choroidal melanomas. Tumor regrowth parameters, tumor cure measurements and histological evaluations will be performed; and 3) to determine the degree of enhancement in PDT induced choroidal vessel destruction and choroid tumor response when experimental rabbits breathe increased oxygen concentrations during PDT.